Rakié Cham

Changes in gait when anticipating slippery floors

Falls precipitated by slipping are listed among the leading causes of injuries. The biomechanical analysis of such events is a necessary component of the slips/falls prevention research. One of the challenges of biomechanical studies is reproducing the unexpected nature of real-life slipping accidents. Thus, the goal of this study was to quantify changes in gait biomechanics when subjects anticipate slippery environments. Foot ground reaction forces and body dynamics of 16 subjects were recorded during level walking and descending ramps of varying frictional properties and inclination. Gait biomechanics were compared among three types of dry trials: (1) baseline (subjects knew the floor was dry); (2) anticipation (subjects were uncertain of the contaminant condition, dry, water, soap or oil); and (3) recovery trials recorded after a contaminated trial (subjects again knew the floor was dry). Subjects were asked to walk as naturally as possible throughout testing. Anticipation trials produced peak required coefficient of friction (RCOF(peak)) values that were on average 16-33% significantly lower than those collected during baseline trials, thus reducing slip potential. During recovery trials, RCOF(peak) values did not return to baseline characteristics (5-12% lower). Postural and temporal gait adaptations, which affected ground reaction forces, were used to achieve RCOF(peak) reductions. Statistically significant gait adaptations included reductions in stance duration (SD) and loading speed on the supporting foot, shorter normalized stride length (NSL), reduced foot-ramp angle and slower angular foot velocity at heel contact. As a result of these adaptations, anticipation of slippery surfaces led to significant changes in lower extremity joint moments, a reflection of overall muscle reactions. Thus, this study suggests that significant gait changes are made when there is a potential risk of slipping even though subjects were asked to walk as naturally as possible. Insights are also gained into the adaptations that are used to reduce the potential of slips/falls.

Biomechanics of Slips

The biomechanics of slips are an important component in the prevention of fall-related injuries. The purpose of this paper is to review the available literature on the biomechanics of gait relevant to slips. This knowledge can be used to develop slip resistance testing methodologies and to determine critical differences in human behaviour between slips leading to recovery and those resulting in falls. Ground reaction forces at the shoe-floor interface have been extensively studied and are probably the most critical biomechanical factor in slips. The ratio of the shear to normal foot forces generated during gait, known as the required coefficient of friction (RCOF) during normal locomotion on dry surfaces or ‘friction used/achievable’ during slips, has been one biomechanical variable most closely associated with the measured frictional properties of the shoe/floor interface (usually the coefficient of friction or COF). Other biomechanical factors that also play an important role are the kinematics of the foot at heel contact and human responses to slipping perturbations, often evident in the moments generated at the lower extremity joints and postural adaptations. In addition, it must be realized that the biomechanics are dependent upon the capabilities of the postural control system, the mental set of the individual, and the perception of the environment, particularly, the danger of slipping. The focus of this paper is to review what is known regarding the kinematics and kinetics of walking on surfaces under a variety of environmental conditions. Finally, we discuss future biomechanical research needs to help to improve walkway-friction measurements and safety.

Lower extremity corrective reactions to slip events.

A significant number of injuries in the workplace is attributed to slips and falls. Biomechanical responses to actual slip events determine whether the outcome of a slip will be recovery or a fall. The goal of this study was to examine lower extremity joint moments and postural adjustments for experimental evidence of corrective strategies evoked during slipping in an attempt to prevent falling. Sixteen subjects walked onto a possibly oily vinyl tile floor, while ground reaction forces and body motion were recorded at 350 Hz. The onset of corrective reactions by the body in an attempt to recover from slips became evident at about 25% of stance and continued until about 45% into stance, i.e. on average between 190 and 350 ms after heel contact. These reactions included increased flexion moment at the knee and extensor activity at the hip. The ankle, on the other hand, acted as a passive joint (no net moment) during fall trials. Joint kinematics showed increased knee flexion and forward rotation of the shank in an attempt to bring the foot back towards the body. Once again, the ankle kinematics appeared to play a less dominant role (compared to the knee) in recovery attempts. This study indicates that humans generate corrective reactions to slips that are different than previously reported responses to standing perturbations translating the supporting surface.

Heel contact dynamics during slip events on level and inclined surfaces

This study describes heel contact dynamics during slip events, information that must be known to develop biomechanically relevant shoe-floor coefficient of friction measurement systems. Sixteen subjects walked on a level, 5 and 10° ramp with two possible contaminants (dry, oil). Foot motion was recorded at 350 Hz and compared among no-slip, slip-recovery and slip-fall events. For all trials, the foot rotated to foot-flat, even during slip and fall trials. Heel sliding patterns recorded upon and shortly after heel contact were similar for all conditions. Slip distances, sliding velocities and heel acceleration profiles varied across trials. During the fall trials, the slipping motion of the foot was found to decelerate approximately 200 to 300 ms into stance before accelerating again, eventually leading to the fall. This deceleration was believed to be an attempt by the subject to recover from the slip. Recovery attempts on inclined surfaces were less successful than on level floors. In general, the slip distance and peak forward sliding velocity associated with fall trials were greater than or equal to 10 cm and 0.8 m/s, respectively. These complex motions at the shoe-floor interface during slipping should be taken into account for improving slip resistance measurement systems.

Gait parameters as predictors of slip severity in younger and older adults

This study investigated the association between slip severity and pre-slip gait characteristics of younger and older subjects. Sixteen younger and eleven older healthy adults walked onto an unexpectedly slippery surface. Slip severity was categorized as either hazardous or non-hazardous using a 1.0 ms peak slip velocity threshold. The results showed that hazardous slips were associated with greater step lengths (normalized by leg length) (SLR), larger and more rapidly changing foot – floor angles (FFA) at heel strike, and increased cadence across the two subject groups. Older subjects were found to walk with shorter SLR and with smaller and more slowly changing FFA at heel strike compared to younger subjects. However, both younger and older subjects experienced hazardous slips at the same rate. A logistic regression model relating SLR and cadence to slip severity predicted that increased SLR and decreased cadence would result in increased probability of hazardous slip (R2 = 0.45, χ2 = 15.30, p<0.01). A second logistic regression model relating FFA with slip severity predicted that increased FFA would result in increased probability of hazardous slip (R2 = 0.53, χ2 = 16.55, p<0.01). These results suggest that gait characteristics prior to foot contact play an important role in the severity of an ensuing slip. The finding that older adults experienced hazardous slips at the same rate as young adults even though their SLR and FFA are smaller suggests that age is also playing a role in other aspects of postural control that impact slip severity.

Effect of flooring on standing comfort and fatigue

This study investigated the influence of flooring on subjective discomfort and fatigue during standing and on potentially related objective measures. Participants stood for 4 h on each of 7 flooring conditions while performing computer tasks. During the 3rd and 4th h, floor type had a significant effect on a number of subjective ratings, including lower-leg and lower-back discomfort/fatigue and 2 of 4 objective variables (center of pressure weight shift and lower-extremity skin temperature). In addition, lower-leg volumetric measurements showed tendencies toward greater lower-extremity swelling on uncomfortable floors. The hard floor and 1 floor mat condition consistently had the worst discomfort/fatigue and objective ratings. Significant relationships were noted between the affected subjective ratings and objective variables. In general, floor mats characterized by increased elasticity, decreased energy absorption, and increased stiffness resulted in less discomfort and fatigue. Thus flooring properties do affect low-back and lower-leg discomfort/fatigue, but the result may be detectable only after 3 h of standing. Potential applications of this research include the reduction of work-related health problems associated with long-term standing.

Validation of a Measure of Smoothness of Walking

BACKGROUND Altered biomechanics and/or neural control disrupt the timing of postures and muscle patterns necessary for smooth and regular stepping. Harmonic ratio of trunk accelerations has been proposed as a measure of smoothness of walking. We sought to validate this measure of smoothness by examining the measure in groups expected to differ in smoothness (ie, young and old) and across walking conditions expected to affect smoothness (ie, straight path, curved path, and dual task). METHODS Thirty young (mean age = 24.4 ± 4.3 years) and 30 older adults (mean age = 77.5 ± 5.1 years) who could ambulate independently participated. We measured linear acceleration of the body along vertical, anterior-posterior, and medial-lateral axes using a triaxial accelerometer firmly attached to the skin over the L3 segment of the lumbar spine during straight path, curved path, and dual task (reciting every other letter of the alphabet) walking. RESULTS Older adults had lower harmonic ratio anterior-posterior (HR(AP)), that is, were less smooth in the direction of motion and walked more slowly than young adults for all walking conditions. Once the analyses were adjusted for walking speed, only HR(AP) differed between young and old participants for all walking conditions. For the most part, both young and old participants were less smooth for slow pace walking, curved path walking, and dual task walking compared with usual pace straight path walking. CONCLUSIONS The harmonic ratio, calculated from trunk acceleration, is a valid measure of smoothness of walking, which may be thought of as a measure of the motor control of walking.

A Randomized Trial of Two Forms of Therapeutic Activity to Improve Walking: Effect on the Energy Cost of Walking

BACKGROUND Therapeutic activities to improve mobility often include walking practice and exercises to improve deficits in endurance, strength, and balance. Because walking may also be energy inefficient in people with decreased mobility, another approach is to reduce energy cost by improving timing and coordination (TC) of movement. METHODS This pilot randomized trial of older adults with slow and variable gait offered two types of therapeutic activity over 12 weeks. One addressed Walking, Endurance, Balance, and Strength (WEBS) and the other focused on TC. Outcomes were energy cost of walking and measures of mobility. RESULTS Of 50 participants (mean age, 77.2 +/- 5.5 years, 65% women), 47 completed the study. Baseline gait speed was 0.85 +/- 0.13 m/s and energy cost of walking was 0.30 +/- 0.10 mL/kg/m, nearly twice normal. Both interventions increased gait speed (TC by 0.21 m/s and WEBS by 0.14 m/s, p < .001). TC reduced the energy cost of walking 0.10 +/- 0.03 mL/kg/m more than WEBS (p < .001) and reduced the modified Gait Abnormalities Rating Scale 1.5 +/- 0.6 more points than WEBS (p < .05). TC had a 9.8 +/- 3.5 points greater gain than WEBS in self-reported confidence in walking (p < .01). CONCLUSIONS In older adults with slow and variable gait, activity focused on TC reduced the energy cost of walking and improved confidence in walking more than WEBS while generating at least equivalent gains in mobility. To optimize mobility, future larger studies should assess various combinations of TC and WEBS over longer periods of time.

The effect of obesity and gender on body segment parameters in older adults

BACKGROUND Anthropometry is a necessary aspect of aging-related research, especially in biomechanics and injury prevention. Little information is available on inertial parameters in the geriatric population that account for gender and obesity effects. The goal of this study was to report body segment parameters in adults aged 65 years and older, and to investigate the impact of aging, gender and obesity. METHODS Eighty-three healthy old (65-75 years) and elderly (>75 years) adults were recruited to represent a range of body types. Participants underwent a whole body dual energy X-ray absorptiometry scan. Analysis was limited to segment mass, length, longitudinal center of mass position, and frontal plane radius of gyration. A mixed-linear regression model was performed using gender, obesity, age group and two-way and three-way interactions (alpha=0.05). FINDINGS Mass distribution varied with obesity and gender. Males had greater trunk and upper extremity mass while females had a higher lower extremity mass. In general, obese elderly adults had significantly greater trunk segment mass with less thigh and shank segment mass than all others. Gender and obesity effects were found in center of mass and radius of gyration. Non-obese individuals possessed a more distal thigh and shank center of mass than obese. Interestingly, females had more distal trunk center of mass than males. INTERPRETATION Age, obesity and gender have a significant impact on segment mass, center of mass and radius of gyration in old and elderly adults. This study underlines the need to consider age, obesity and gender when utilizing anthropometric data sets.

Simulating balance recovery responses to trips based on biomechanical principles

To realize the full potential of human simulations in interactive environments, we need controllers that have the ability to respond appropriately to unexpected events. In this paper, we create controllers for the trip recovery responses that occur during walking. Two strategies have been identified in human responses to tripping: impact from an obstacle during early swing leads to an elevating strategy, in which the swing leg is lifted over the obstacle and impact during late swing leads to a lowering strategy, in which a swing leg is positioned immediately in front of the obstacle and then the other leg is swung forward and positioned in front of the body to allow recovery from the fall. We design controllers for both strategies based on the available biomechanical literature and data captured from human subjects in the laboratory. We evaluate our controllers by comparing simulated results and actual responses obtained from a motion capture system.